Fix #8802: Use wildcards for result type approximation of implicits #8824
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Use wildcards for result type approximation of dependent implicit methods. In a situation like ``` def f(using x: T): C[x.Out] ``` we need to go constrain the result type of `f` before doing the implicit search for `T`. Previously we created a fresh type variable `param(1)` with `T & Singleton` as upper bound. That works well for other uses of result type approximation, but in this case, we miss constraining `param(1)` from below by the result of the implicit search. So in the end `param(1)` gets interpolated to its upper bound, which leads to problems. One possible solution is to add the missing lower constraint for the dependent type variable. But it's easier to just use a Wildcard type, which is what this PR does.
smarter
requested changes
Apr 28, 2020
smarter
reviewed
Apr 28, 2020
Co-Authored-By: Guillaume Martres <[email protected]>
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Also fixes #8825 |
smarter
approved these changes
Apr 28, 2020
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Use wildcards for result type approximation of dependent implicit methods.
In a situation like
we need to go constrain the result type of
fbefore doing the implicitsearch for
T. Previously we created a fresh type variableparam(1)withT & Singletonas upper bound. That works well for other uses ofresult type approximation, but in this case, we miss constraining
param(1)from below by the result of the implicit search. So in the endparam(1)gets interpolated to its upper bound, which leads to problems.One possible solution is to add the missing lower constraint for the dependent
type variable. But it's easier to just use a Wildcard type, which is what
this PR does.